Fingerprint sensor and method

[0002] This application is a continuation-in-part application for two prior filed and currently pending U.S. patent applications, Ser. No. 09/339,464 filed Jun. 23, 1999, now U.S. Pat. No. 6,191,410 and Ser. No. 09/444,131 filed Nov. 19, 1999.

[0003] This invention is in the field of three dimensional object sensing apparatuses and methods and more particularly in the field of apparatuses and methods for sensing fingerprints.

[0004] Fingerprint sensing devices typically consist of a glass plate or prism upon which the finger of the subject is pressed, an illuminating light source which directs the light through the prism to the contact zone between the finger and the glass plate or prism, an image producing lens and an image capturing device such as a charge couple device (CCD). Most of these known devices function on the basic principle that if the angle of incidence of the illuminating light with the contact zone between the finger of the subject and the glass plate or prism, is adjusted to within a certain range which is dependent on the frequency of the light used, the illuminating light will be internally reflected from the contact zone at fingerprint valley points where there is no contact between the finger and the glass surface, and will not be internally reflected from the ridge points where the finger contacts the glass surface. The reflected light is focused into an image by an image producing lens and the image is transformed into an electrical signal by a CCD or other sensing device.

[0005] These known devices have inherent problems and limitations relating to the accuracy of the valley and ridge information defining the subject fingerprint. Known methods require the use of an image producing lens and require an optical sensor such as a CCD to receive the image and convert it to an electrical signal. Improvements are needed in the means and method of illuminating the contact zone between the finger and glass surface, the physical geometry of the sensing unit and the means and method of receiving and digitizing the fingerprint information.

[0006] An object of the present invention is to provide a simpler, more accurate and more reliable method and apparatus for extracting and digitizing a fingerprint for imaging and identification purposes. It is a further object of the present invention to provide a method and apparatus for utilizing an array of light-emitting diodes (LED's) for emitting point source radiation as the source of illuminating radiation. It is a further object of the present invention to provide a fingerprint sensing device that is durable, inexpensive and simpler to manufacture and maintain. It is a further objective of the present invention to provide an apparatus and method for the direct digitization of a fingerprint without the use of an image producing lens and optical image sensor.

[0007] Preferred embodiments of the apparatus of the present invention comprise a prism, a pixilated source of radiation, and a photoelectric sensor. For certain preferred embodiments, the prism is wedge-shaped, but it can be of any shape that provides for differentiation between fingerprint ridges and valleys. The finger of the subject is pressed to the prism top surface. For certain preferred embodiments, an LED array, which is used as the pixilated radiation source, lines the prism bottom surface and the photoelectric sensor lines the prism end surface. However, the pixilated source of radiation can be any array of point source radiation emitters which can be focused respectively on selected points of illumination on the prism top surface.

[0008] For preferred embodiments using an LED array, the LED's of the LED array are arranged in a grid network with the spacing between the LED's being selected to provide for the desired accuracy of the fingerprint extraction and digitization. Each of the LED's emits a sub-beam into the prism bottom surface when activated and each of these LED's corresponds to a point of illumination on the prism top surface. The wedge angle between the prism top surface and the prism bottom surface determines the angle of incidence for each of the sub-beams. The angle of incidence of the sub-beams is selected so that the points where the fingerprint ridges of the subject contact the prism top surface will not internally reflect the LED radiation, and the points corresponding to the fingerprint valleys of the subject where the finger of the subject does not contact the prism top surface will reflect the radiation.

[0009] Each LED of the LED array is activated in a desired sequence thereby transmitting the light into the bottom surface of the prism and illuminating a corresponding point on the top contact surface of the prism. However, the illuminating radiation is not confined to the corresponding point of illumination. Accordingly the photoelectric sensor will receive reflected radiation for each LED. If the LED corresponds to a fingerprint ridge point, the amount of illuminating radiation reflected to a photoelectric cell will be measurably less than that reflected if the LED corresponds to a fingerprint valley point. The difference can be increased by incorporating a minute lens at each LED point. The lenses are fixed to the LED array or the prism or are interposed between the LED array and the prism as a lens wafer. The lenses can also be incorporated as an integral part of the prism. These lenses provide for the focusing of the radiation transmitted from each LED on the corresponding point of illumination on the top contact surface of the prism. For these embodiments, the non-reflection of the illuminating radiation will be near total from fingerprint ridge points and the reflection of the illuminating radiation will be near total for the fingerprint valley points, thereby enhancing differentiation between ridge points and valley points. The number of pixels and thus the accuracy of the resolution of the fingerprint extraction, is determined by the density of the LED's.

[0010] For some embodiments, each sub-beam is reflected to a unique point on the photoelectric sensor. The photoelectric sensor may have a grid of receptors, each receptor sensing the reception of a sub-beam. The reception or non-reception of a sub-beam indicates a fingerprint valley or ridge at the corresponding point of illumination. For other embodiments, the sub-beams may be emitted sequentially in a burst and therefore sensed sequentially by a single-receptor photoelectric sensor. Each sub-beam received in its assigned time slot indicates a fingerprint valley at its corresponding point of illumination and each sub-beam not received in its assigned time slot indicates a fingerprint ridge at its corresponding point of illumination. Either version provides for a very accurate digitization of the fingerprint, which can then be used for imaging or identification purposes. This provides for the direct digitization of the subject fingerprint without the need for an image producing lens or an optical image sensing device.

[0011] The photoelectric sensor may have a filter or may be tuned to detect only the frequency of radiation emitted by the LED so as to prevent interference from radiation from other sources. Alternatively, filters or shields may be installed on all exposed exterior surfaces of the prism to prevent admission of radiation to the prism from any source other than the surface emitting laser.

[0012] For any of the foregoing embodiments, the fingerprint apparatus of the present invention may be connected to an external computer to process the data, or may be equipped with its own computer circuit, particularly for remote applications.

[0013] For any of the foregoing embodiments, an additional lens or lens arrangement, a sensor lens, may be included between the prism and the photoelectric sensor, to provide for focusing the reflected radiation for sensing. This allows the use of a smaller photoelectric sensor or a smaller grid of receptors for the photoelectric sensor. The sensor lens may be affixed to or incorporated into the prism end surface, or may be interposed between the prism and the photoelectric sensor.

[0014] The following drawings illustrate preferred embodiments of the apparatus of the present invention.

[0015] FIG. 1 is a side view perspective of a preferred embodiment of the apparatus of the present invention utilizing an LED array.

[0016] FIG. 2 is a side view of a preferred embodiment of the apparatus of the present invention utilizing a LED array.

[0017] FIG. 3 is a side view of a preferred embodiment of the apparatus of the present invention utilizing a LED array and having a sensor lens.

[0018] Embodiments of the present invention utilize pixilated means for internally illuminating points of illumination on a contact surface of a prism. The pixilated source of radiation can be any array of point source radiation emitters which can be focused respectively on selected points of illumination on the contact surface.

[0019] Referring first to FIG. 1, a preferred embodiment of the apparatus of the present invention which comprises a wedge-shaped prism 1, an LED array 27, and a photoelectric sensor 3, is illustrated therein. Referring also to FIG. 2, a finger 4 of the subject is pressed to the top prism top surface 5, the contact surface, contacting the prism top surface in a contact zone 18. The LED array, having a network of LED's 28, is affixed to the prism bottom surface 7 and the photoelectric sensor is affixed to the prism end surface 8. Preferred embodiments will also incorporate a lens wafer 23 interposed between the LED array and the prism bottom surface. The LED's are arranged in a grid network 9 with a spacing 10 between the LED's being selected to provide for the desired accuracy of the fingerprint extraction and digitization. Each of the LED's emits an LED sub-beam 29 which passes through the lens wafer into the prism bottom surface. The wedge angle 13 between the prism top surface and the prism bottom surface determines the angle of incidence 14 for each of the LED sub-beams. The angle of incidence of the sub-beams is selected so that the points where the fingerprint ridges 15 of the subject contact the prism top surface will not internally reflect the LED radiation, and the points corresponding to the fingerprint valleys 16 of the subject where the finger of the subject does not contact the prism top surface will reflect the LED radiation.

[0020] While certain preferred embodiments utilize a wedge shaped prism as illustrated in FIGS. 1, 2, and 3, other embodiments may utilize prisms with a different shape or may utilize any medium which allows for the internal reflection of illuminating radiation at an angle which will provide for differentiation of the fingerprint ridges and valleys.

[0021] Each of the LED sub-beams is correlated with and focused upon a unique illumination point 17 on the prism top surface. Similarly, except for those points in the contact zone 18 where the fingerprint ridges of the subject contact the prism top surface, each LED sub-beam is reflected to a unique sensing point 19 on the photoelectric sensor. The number of pixels and thus the accuracy of the resolution of the fingerprint extraction, is determined by the density of the LED's in the LED array. Referring to FIG. 3, for some embodiments, a sensor lens 26 focuses the reflected sub-beam radiation on the photoelectric sensor. The sensor lens may be affixed to or incorporated in the prism end surface or may be interposed between the prism and the photoelectric sensor.

[0022] The sub-beams may be emitted sequentially in a burst and therefore sensed sequentially by a single-receptor photoelectric sensor. The photoelectric sensor may have a filter 20 or may be tuned to detect only the frequency of radiation emitted by the LED array so as to prevent interference from radiation from other sources. Alternatively, filters or shields may be installed on all exposed exterior surfaces of the prism to prevent admission of radiation to the prism from any source other than the LED array. The intensity of the radiation received for each sub-beam in its assign time slot indicates a fingerprint valley or a fingerprint ridge at its corresponding point of illumination. Each pixel of the LED array is activated in a desired sequence thereby transmitting the illuminating radiation through the lens wafer into the bottom surface of the prism and illuminating a corresponding point on the top contact surface of the prism. However, the LED sub-beam illuminating radiation may not be confined to the corresponding discreet point of illumination. Accordingly, the photoelectric sensor will receive reflective radiation for each LED pixel. If the pixel corresponds to a fingerprint ridge point the amount of illuminating radiation reflected to the photoelectric cell will be measurably less than that reflected if a pixel corresponds to a fingerprint valley point. The difference is substantially increased through incorporating a minute lens at each pixel point which is contained in the lens wafer. Alternatively these lenses can also be affixed to the LED array or the prism. These lenses provide for the focusing of the radiation emitted by each pixel of the LED array on the corresponding point of illumination on the top contact surface of the prism. The focal length of the lenses varies based upon the LED location, to provide for focusing on the point of illumination. For these embodiments, the percentage of non-reflection of the illuminating radiation will be high from fingerprint ridge points and the percentage of reflection of the illuminating radiation will be high for the fingerprint value points. This enhances differentiation between ridge points and valley points.

[0023] Alternatively the photoelectric sensor may have a grid of receptors or sensors, each receptor or sensor being used for sensing the reception of radiation of a unique sub-beam. For these embodiments, the sub-beams can be emitted simultaneously. The reception or non-reception by the correlated sensor of a specified intensity of radiation from the sub-beam indicates a fingerprint valley or ridge at the corresponding point of illumination. A sensor lens will reduce the size of the photoelectric sensor or the size of the grid of receptors needed for the photoelectric sensor.

[0024] The photoelectric sensor generates electric signals based upon the sub-beams received or the intensity of the radiation received for each sub-beam. Any of the preferred embodiments of the apparatus of the present invention described above provides for a very accurate digitization of the fingerprint, which can then be used for imaging or identification purposes. Each of these embodiments provides for the direct digitization of the subject fingerprint without the need for an image producing lens or an optical image sensing device.

[0025] Any of the preferred embodiments of the fingerprint sensing apparatus of the present invention may be connected to an external computer to control the emission of the sub-beams and to process the electric signals generated by the photoelectric sensor or sensors, or may be equipped with its own computer circuit, particularly for remote applications where a support computer with required software is not available.

[0026] Other embodiments of the invention and other variations and modifications of the embodiments described above will be obvious to a person skilled in the art. Therefore, the foregoing is intended to be merely illustrative of the invention and the invention is limited only by the following claims.